EMBODIED CARBON IN GREEN RATING SYSTEMS

Building and Material Reuse:

For this credit, structural engineers can help the project team identify potential reusable or salvageable structural elements. By reusing structural elements in existing buildings, the structural system’s overall embodied carbon footprint is reduced due to the mitigation of carbon released during manufacturing and transporting new structural materials to the construction site. Up to four credits can be achieved depending on the percentage of existing walls, floors, and roof reused relative to the total floor area. In addition, salvaged or reused materials from offsite are allowed to be counted as reuse within this credit. For example, using salvaged timber or steel beams from another building and incorporating it into a the project would count as offsite reuse that is eligible for this credit. Reuse need not be the same material used as the same original function (a salvaged structural beam can be reused as a decorative finish or for other nonstructural purposes, for example). Teams should consider this strategy when offsite salvage materials are available, or if the project needs some additional reused materials to hit a higher credit achievement threshold. 

Whole Building Life-Cycle Assessment:

As part of the WBLCA, structural engineers can run a Life Cycle Analysis (LCA) on the structural design to help identify areas of high environmental impacts and provide embodied carbon measurements. Just conducting a WBLCA for the project’s structure and enclosure can help the project team achieve one LEED point. If the WBLCA demonstrates a reduction in global warming potential (GWP) of 5% or 10% compared to the baseline building, the project can obtain two or three LEED points, respectively. For a WBLCA on the project’s structure and enclosure demonstrating at least a 20% reduction for GWP and a 10% reduction in two additional impact categories, the team can obtain four LEED points (however, projects must incorporate some reuse materials to be eligible for the fourth point). Early in the design phase, the design team should agree on which consultant should include the WBLCA for the baseline building in their scope. For additional information on developing the baseline building for a WBLCA, see “Whole Building Life Cycle Assessment: Reference Building Structure and Strategies” published by the ASCE SEI Sustainability Committee and the LEED V4.1 Building Design and Construction Guide.

Environmental Product Declarations:

Under this credit, structural engineers have the opportunity to help the project team achieve two LEED points. One credit is earned if 20 EPDs from five different manufacturers are submitted. Almost all structural materials have either a product-specific Type III EPD or industry-wide Type III EPD obtained from the material supplier. Product-specific Type III EPDs are weighted with a factor of one or 1.5 depending on if they were internally or externally reviewed by a third-party, respectively. An industry-wide Type III EPD is weighted with a factor of one. Therefore, it is beneficial for the industry and LEED project to obtain product-specific Type III EPDs that provide a more accurate picture of the environmental effects of a manufacturer’s product in order to quantify the total embodied carbon impact of a building. By asking structural material manufacturers for product-specific EPDs, structural engineers can drive the market towards transparency regarding the environmental impacts of the materials engineers specify on their projects.

An additional credit can be earned by selecting Embodied Carbon/LCA Optimization reports for five products from three different manufacturers. One such report type is an action plan that is published by manufacturers, as well as optimized EPD reports based on product improvement in embodied carbon impacts over time. As a significant number of conditions impact the weighting of individual reports, the LEED V4.1 Building Design and Construction Guide documentation should be consulted for further details.

Structural engineers can specify:

1) Structural timber certified by the Forest Stewardship Council (FSC) or USGBC approved equivalent,

2)  Employ reused or salvaged materials, and

3) Utilize structural materials with recycled content to achieve two LEED points.

Research has shown that timber harvested from responsibly managed forests, like FSC Certified wood, can contribute to a lower embodied carbon footprint than non-certified timber. Reusing existing structural materials on a project can help reduce the demand for new materials and the structure’s embodied carbon from extraction and manufacturing (note: if salvaged or reused materials from offsite are incorporated into the project, they cannot be double counted in this credit and the Building Life-Cycle Impact Reduction credit). Structural engineers will need to assess and determine the condition and strength of existing structural elements to ensure they will be adequate for the demands of the proposed design. It is paramount that structural engineers are engaged during schematic design when building and material reuse is a design option.

This pilot credit is an alternative compliance path to the Material & Resource Credit: Sourcing of Raw Materials. This pilot credit requires 100% of structural framing lumber is from legal sources as defined by ASTM D7612-10 and 70% (based on cost) of all wood is from responsible sources as defined by ASTM D7612-10. Sourcing timber from legal and responsible sources helps protect forests from unsustainable harvesting and managing practices and ensures forests continue to promote biodiversity and carbon sequestering.

For the project team to be awarded points for this pilot credit, the structural engineer can  provide the team with the following information:

• Material embodied carbon intensity baselines (mECIb)
• Actual material embodied carbon intensities (mECIa)
• Building embodied carbon intensity baseline (bECIb)
• Actual building embodied carbon intensity (bECIa)

Structural materials included in the pilot credit are concrete, steel, timber, and metal framing. The engineer shall obtain the structural material quantities used for calculations from 100% CD Construction estimate, 100% CD BIM bill of materials, or the contractor’s material quantity take-offs.

The mEBIb is determined by multiplying the structural material quantities by the material embodied carbon baseline values published by the University of Washington – Carbon Leadership Forum (or other approved data provider). The sum of all materials required to be accounted for in the baseline is then taken as the bEClb. To calculate the mECIa, the structural material quantities are multiplied by GWP numbers from third-party verified Environmental Product Declaration with the applied University of Washington – Carbon Leadership Forum methodology. The sum of mECIa is taken as the bECa and compared to the building embodied carbon intensity baseline (bEClb). If the percent difference between the bECIb and the bECIa is between zero to 30%, one point is awarded. If the percent difference is greater than 30%, two points are rewarded.

It is beneficial for the industry to ask and obtain EPD’s for structural materials to drive the market towards transparency and prioritization of low embodied carbon materials.

United States Green Building Council (USGBC). (2020). LEED Building Design and Construction Guide, Version 4.1. Washington, DC. Accessed June 30, 2021. https://build.usgbc.org/bd+c_guide